Electrode array and method of placement

ABSTRACT

A headset for detecting brain electrical activity may include a flexible substrate having first and second ends each configured to engage an ear of a subject and dimensioned to fit across the forehead of a subject. The headset may also include a plurality of electrodes disposed on the substrate and configured to contact the subject when the headset is positioned on the subject. First and second electrodes may contact top center and lower center regions of the forehead, respectively, third and fourth electrodes may contact front right and front left regions of the forehead, respectively, fifth and sixth electrodes may contact right side and left side regions of the forehead, respectively, and electrodes included within the securing devices may contact the ear regions. The third and fourth electrodes may be moveable in at least a vertical direction relative to the other electrodes.

I. DESCRIPTION

1. Field of the Disclosure

Embodiments of the present disclosure relate to, among other things,medical devices and, in particular, to an electrode array for sensingbrain electrical activity and a method of placing electrodes.

2. Background of the Disclosure

The central nervous system (CNS), and the brain in particular, performsome of the most complex and essential processes in the human body.Surprisingly, contemporary health care often lacks the tools toobjectively and effectively assess brain function at the point-of-care.A person's mental and neurological status is typically assessed using aninterview and a subjective physical exam. Clinical laboratories may nothave the capacity to effectively assess brain function or pathology, andmay be largely limited to the identification of poisons, toxins, drugs,or other foreign substances that may have impacted the central nervoussystem (CNS).

Brain imaging technologies, such as computed tomography imaging (CT),magnetic resonance imaging (MRI), positron emission tomography (PET),and single photon emission computerized tomography (SPECT) may be usedto visualize the structure of the brain. Yet these anatomical tests mayreveal little information about brain function. For example,intoxication, concussion, active seizure, metabolic encephalopathy,infections, diabetic coma, and numerous other conditions may show noabnormality on a CT scan. Even a stroke or a traumatic brain injury(TBI) may not be immediately visible in an imaging test, even when aperson has dearly observable abnormal brain function. CT and MRI mayonly detect a change in brain function after the morphology or structureof the brain has changed. Thus, in some cases, it may take hours or daysafter the onset of a condition before severe neurological pathology isvisible on the CT or MRI.

Such limitations may be especially significant after trauma, because thebrain may require immediate attention to avoid further deterioration.For example, diffuse axonal injury (DAI), related to shearing of nervefibers and present in many concussive brain injury cases, may remaininvisible on most routine structural images. If undetected at an earlystage, swelling or edema from DAI may lead to coma and death.

Functional MRI (fMRI), a recent improvement over MRI, provides relativeimages of the concentration of oxygenated hemoglobin in various parts ofthe brain. While the concentration of oxygenated hemoglobin may be auseful indication of the metabolic function of specific brain regions,it may provide limited or no information about the underlying brainfunction, i.e., the processing of information by the brain, which iselectrochemical in nature. Another recent improvement, diffusion MRI(dMRI) maps the diffusion process of molecules, such as water, in thebrain and may provide details about tissue architecture. One type ofdMRI, diffusion tensor imaging (DTI), has been used successfully toindicate abnormalities in white matter fiber structure and to providemodels of brain connectivity. DTI may provide a viable imaging tool forthe detection of DAI, but such imaging again focuses on anatomicalinformation rather than brain function.

All of the brain's activity, whether sensory, cognitive, emotional,autonomic, or motor function, is electrical in nature. Through a seriesof electrochemical reactions, mediated by molecules calledneurotransmitters, electrical potentials (voltages) are generated andtransmitted throughout the brain, traveling continuously between andamong a myriad of neurons. This activity establishes the basicelectrical signature of the electroencephalogram (EEG) and createsidentifiable frequencies that may have a basis in anatomic structure andfunction. Understanding these basic rhythms and their significance maymake it possible to characterize the electrical brain signals as beingwithin or beyond normal limits. At this basic level, the electricalsignals may serve as a signature for both normal and abnormal brainfunction. Just as an abnormal electrocardiogram (ECG) pattern is astrong indication of a particular heart pathology, an abnormal brainwave pattern may be a strong indication of a particular brain pathology.Additionally, the electrical activity of the brain may be affectedcloser to the onset of a condition, before any structural changes haveoccurred.

Even though EEG-based neurometric technology is generally accepted todayin neurodiagnostics, its application in the clinical environment isnotably limited. Using standard EEG technology, it may take a skilledtechnician 1 to 4 hours to administer a test. A neurologist must theninterpret the data and make a clinical assessment.

Furthermore, some equipment used for recording EEG data may be too bulkyor may be inappropriate for certain situations. For example, standardEEG equipment may require a technician to individually apply 19 or moreelectrodes onto the scalp of a subject. Each electrode must be placeddirectly onto the scalp of the subject (often with a conductive gel orpaste) in the correct location on the subject's head. Applying theelectrodes, each with its own lead wire, may be tedious and timeconsuming, taking thirty minutes or longer to complete. Application maybe further complicated because the electrode wires may easily becometangled and may interfere with other operations. The lack of portabilityof EEG technology may make it infeasible for point-of-care applications.

To make EEG technology easier to apply to a subject, some products haveincorporated electrodes into nets or caps that may be placed on thesubject's head. Once in position, a technician can then individuallyplace and attach each electrode to the scalp. While this may decreasepreparation time, it still requires a technician to place eachelectrode.

Other products have tried to eliminate the need to individually placeeach electrode by allowing an administrator to apply all of theelectrodes at once to a subject. Such products fix the relativepositioning of electrodes in a headset, which may then be fitted to thesubject. Thus, by incorporating all of the electrodes into a headset andfixing their relative location, placement of the electrodes is completeonce the headset is positioned on the subject, substantially reducingthe preparation time. Such technology has worked to some extent foranesthesiologists in sedation applications, for example, to detectwhether a person's EEG readings indicate proper sedation based onpre-sedation and post-sedation readings of that same person. Yet,grouping the electrodes in this manner has proven surprisinglyinadequate and unreliable for capturing EEG readings capable ofdiscriminating between levels of normal versus abnormal brain activityfor a given person relative to a population.

Without a quick and reliable way of placing electrodes for EEG readings,current EEG equipment and electrode arrays may not be practical for theemergency room (ER), operating room (OR), intensive care unit (ICU),first response situations, sporting events, the battlefield, or otherpoint-of-care settings and situations. Thus, there is an immediate needfor a portable brain state assessment technology to provide rapidneurological evaluation and treatment guidance for subjects with acutebrain injury or disease, so as to prevent further brain damage anddisability. This in turn may help medical personnel select an immediatecourse of action, prioritize people for imaging, and determine whetherimmediate referral to a neurologist or neurosurgeon is required.

Embodiments of the disclosure described herein may overcome somedisadvantages of the prior art.

II. SUMMARY OF THE DISCLOSURE

Embodiments of the present disclosure relate to medical devices, such asthe placement of electrodes on a subject for sensing brain electricalactivity. Various embodiments of the disclosure may include one or moreof the following aspects.

In accordance with one embodiment, a headset for detecting brainelectrical activity may include a flexible substrate dimensioned to fita forehead of a subject. The substrate may have a first end and a secondend each configured to engage an ear of a subject to position thesubstrate across the forehead. The substrate may include at least oneexpansible region permitting a distance between the first and secondends to selectably vary. The headset may also include a plurality ofelectrodes disposed on the substrate so that the electrodes contact thesubject when the headset is positioned on the subject. A first electrodemay be configured to contact a top center region of the forehead, asecond electrode may be configured to contact a lower center region ofthe forehead, a third electrode may be configured to contact a frontright region of the forehead, a fourth electrode may be configured tocontact a front left region of the forehead, a fifth electrode may beconfigured to contact a right side region of the forehead, and a sixthelectrode may be configured to contact a left side region of theforehead. One electrode may be included within each securing device andconfigured to contact an ear region of the subject when the headset ispositioned on the subject, and at least the third and fourth electrodesmay be moveable in at least a vertical direction relative to the otherelectrodes when the headset is positioned on the subject. The headsetmay also include flexible circuitry in the substrate operably coupled tothe electrodes.

Various embodiments of the headset may include one or more of thefollowing features: at least one of the plurality of electrodes may begrounded; at least the third and fourth electrodes may each include adistance indication gauge; the distance indication gauge may include atab with a first end connected to the electrode and a second free endextending from the electrode; the distance from the second end of thedistance indication gauge to a center of the electrode may substantiallyequal the distance that the electrode is located from an anatomicalfeature of the subject; the anatomical feature may be an eyebrow; andthe at least one expansible region may include a flexure or corrugationin the substrate.

In accordance with another embodiment, a method of applying a headsetmay include: applying a first sensor to a left ear region, applying asecond sensor to a right ear region, applying a third sensor to an uppercenter region of the forehead, applying a fourth sensor to the forehead,applying a fifth sensor to a left frontal region of the forehead,applying a sixth sensor to a right frontal region of the forehead,applying a seventh sensor to a left side region of a forehead, applyingan eighth sensor to a right side region of the forehead, wherein theheadset includes a flexible substrate dimensioned to fit the forehead ofthe subject having a first end and a second end, wherein the first endand the second end each includes a securing device configured to engagean ear of the subject to position the flexible substrate across theforehead, wherein the flexible substrate includes at least one distancegauge configured to indicate the distance from an anatomical region ofthe subject from which to apply at least one sensor, and wherein theheadset includes a connector region, and the method further includesconnecting the connector region to a processor.

Various embodiments of the method may include one or more of thefollowing features: the connecting may include wirelessly or physicallyconnecting the connector region to the processor; the processor may behoused in a portable handheld device and configured to receive data fromat least one sensor; the method may further include conducting animpedance check, wherein the portable handheld device transmits at leastone signal to each sensor and measures a resulting current from eachsensor to identify an impedance value for each sensor; the portablehandheld device may include a display screen for displaying theimpedance value for each sensor and the method may further includecomparing the identified impedance value for each sensor to apredetermined impedance range to determine whether the impedance valuefalls within the range and adjusting any sensor that has an impedancevalue that falls outside of the range to cause the impedance value forthat sensor to fall within the range; the substrate may include at leastan expansible region permitting a distance between the first end and thesecond end to selectably vary; the fourth sensor may be applied to alower center region of the forehead of the subject and the fourth sensormay be grounded; the anatomical region of the subject may be an eyebrow;a first distance gauge may include a tab extending from a lower regionof the fifth sensor and a second distance gauge may include a tabextending from a lower region of the sixth sensor; applying the fifthsensor and applying the sixth sensor may include adjusting therespective tabs so that a distal region of the tabs sits directly abovethe eyebrows without touching the eyebrows; at least one sensor may beremovable; applying the third sensor may include placing the thirdsensor below a hairline of the subject; the anatomical region may be anasion of the subject; and the distance gauge may include an elongatedsection extending from the fourth sensor and applying the fourth sensormay include positioning the distance gauge so that a distal portion ofthe distance gauge is directly above the nasion.

In accordance with another embodiment, a headset for detecting brainelectrical activity may include: a flexible substrate dimensioned to fita forehead of a human subject having a first end and a second end,wherein the first end and the second end each includes a securing deviceconfigured to engage an ear of the subject to position the flexiblesubstrate across the forehead, and wherein the flexible substrateincludes at least one expansible region permitting a distance betweenthe first end and the second end to selectably vary; a first sensordisposed on the flexible substrate and configured to contact an uppercenter region of the forehead when the headset is positioned on thesubject; a second sensor disposed on the flexible substrate andconfigured to contact a lower center region of the forehead when theheadset is positioned on the subject; a third sensor disposed on theflexible substrate and configured to contact a left frontal region ofthe forehead when the headset is positioned on the subject, wherein theheadset is adjustable such that the position of the third sensor ismovable relative to the position of the first sensor; a fourth sensordisposed on the flexible substrate and configured to contact a rightfrontal region of the forehead when the headset is positioned on thesubject, wherein the headset is adjustable such that the position of thefourth sensor is movable relative to the position of the first sensor; afifth sensor disposed on the flexible substrate and configured tocontact a left side region of the forehead when the headset ispositioned on the subject; a sixth sensor disposed on the flexiblesubstrate and configured to contact a right side region of the foreheadwhen the headset is positioned on the subject; a seventh sensor disposedon the first end of the flexible substrate and configured to contact aleft ear region of the subject when the headset is positioned on thesubject; and an eighth sensor disposed on the second end of the flexiblesubstrate and configured to contact a right ear region of the subjectwhen the headset is positioned on the subject, wherein the secondsensor, the third sensor, and the fourth sensor each includes anelongated portion having a first end connected to the sensor and a freeend extending from the sensor.

Further, a method of applying this headset may include: positioning thefree end of the elongated portion of the second sensor at a nasionregion of the subject to align the second sensor and the first sensor onthe forehead; adjusting the location of the first sensor so that thefirst sensor is located on the forehead below a hairline of a subject;attaching the first sensor and the second sensor to the forehead of thesubject; engaging the first end with a first ear region of the subject;engaging the second end with a second ear region of the subject;attaching the seventh sensor to the first ear region and attaching theeighth sensor to the second ear region; positioning the free end of theelongated portion of the third sensor directly above a first eyebrow ofthe subject so that the free end does not touch the first eyebrow andattaching the third sensor to the forehead of the subject; positioningthe free end of the elongated portion of the fourth sensor directlyabove a second eyebrow of the subject so that the free end does nottouch the second eyebrow and attaching the fourth sensor to the foreheadof the subject; attaching the fifth sensor to the forehead of thesubject; and attaching the sixth sensor to the forehead of the subject.

III. BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings illustrate certain embodiments of the presentdisclosure, and together with the description, serve to explainprinciples of the present disclosure.

FIG. 1 depicts an exemplary brain assessment system, in accordance withan embodiment of the present disclosure;

FIG. 2A depicts an exemplary arrangement of sensors, in accordance withan embodiment of the present disclosure;

FIG. 2B depicts an exemplary array that may be used with the brainassessment system of FIG. 1;

FIG. 3 depicts an exemplary array, in accordance with an embodiment ofthe present disclosure;

FIG. 4A depicts a side view of the exemplary array of FIG. 3 when fittedon a subject, in accordance with an embodiment of the presentdisclosure;

FIG. 4B depicts a front view of the exemplary array of FIG. 3 in a firstposition when fitted on a subject;

FIG. 4C depicts a front view of the exemplary array of FIG. 3 in asecond position when fitted on a subject;

FIG. 5 depicts an exemplary array, in accordance with an embodiment ofthe present disclosure;

FIGS. 6A through 6C illustrate graphical comparisons of differentfeatures of different signal properties measured using free electrodes,a fixed headset, and an exemplary array according to an embodiment ofthe present disclosure; and

FIG. 7 illustrates a graphical representation of electrode location foran exemplary array according to an embodiment of the present disclosure.

IV. DETAILED DESCRIPTION OF EMBODIMENTS

Reference will now be made in detail to the embodiments of the presentdisclosure described below and illustrated in the accompanying drawings.Wherever possible, the same reference numbers will be used throughoutthe drawings to refer to same or like parts.

While the present disclosure is described herein with reference toillustrative embodiments for particular applications, it should beunderstood that the disclosure is not limited thereto. Those havingordinary skill in the art and access to the teachings provided hereinwill recognize additional modifications, applications, embodiments, andsubstitutions of equivalents all fall within the scope of the invention.Accordingly, the disclosure is not to be considered as limited by theforegoing or following descriptions.

Other features and advantages and potential uses of the presentdisclosure will become apparent to someone skilled in the art from thefollowing description of the disclosure, which refers to theaccompanying drawings.

In an exemplary embodiment, data corresponding to electrical brainactivity may be used to detect neurological injury and/or disease insubjects. FIG. 1 depicts one embodiment of a neuro-assessment apparatus10 for acquiring and processing electrical brain signals and evaluatinga subject's neurological condition. In some embodiments,neuro-assessment apparatus 10 may be implemented as a portable devicefor point-of-care applications. Apparatus 10 may include a base unit 42,which may be configured either as a handheld unit or as larger,stationary unit. Base unit 42 may be capable of storing, processing, orfurther transmitting data corresponding to electrical brain activity.For example, base unit 42 may include an analog electronics module 30and a digital electronics module 50 for receiving and converting EEGsignals, a processor 51, a memory 52, a user interface 46 for allowinguser input and for outputting data to a user, and a rechargeable and/orreplaceable battery 44 for powering apparatus 10. If rechargeable,battery 44 may interface with a charger 39, which in turn may beconnectable to an AC power source 37, which may also include appropriatefiltering of powerline noise components that could impact signalquality. Further, base 42 may be configured to transmit and/or receivedata from any number of suitable components external to apparatus 10,e.g., a printer 49, an external memory 47, or an external processor 48.Memory 47 and/or processor 48 may be included in the same component orin different components, e.g., a computer, a smartphone, a largerdatabase system, a patient monitoring system, etc. Further, base 42 maybe operably coupled to these external components either through a hardconnection or wirelessly.

Apparatus 10 may also include a subject sensor 40 operably coupled tobase unit 42, either by a hard connection or wirelessly. Subject sensor40 may be configured to detect EEG signals from the subject and transmitthis data to base 42, as indicated by arrow 41 a. In some embodiments,subject sensor 40 may include an electrode array 20 with one or moredisposable neurological sensors, such as electrodes, configured toattach to a subject's head for acquiring electrical brain signals. Theelectrodes may be configured for sensing spontaneous electrical brainactivity and/or evoked potentials generated in response to appliedstimuli (e.g. auditory, visual, tactile, etc.), as depicted by optionalstimuli generator 54 in base 42, stimulus delivery device 31 eitherincorporated into or separate from subject sensor 40, and arrow 41 brelaying signals between the two.

In one embodiment, array 20 may include 8 electrodes, for example, fiveactive channels and three reference channels. Array 20 may includeanterior (frontal) electrodes Fp1, Fp2, F7, F8, AFz (also referred to asFz′) and FPz (ground electrode) configured to attach to a subject'sforehead, and electrodes A1 and A2 configured to attach to the front orback side of the ear lobes, or on the mastoids, roughly in accordancewith the International 10/20 electrode placement system (with theexception of AFz), as is shown in FIG. 2A.

While the International 10/20 system typically requires at least 19electrodes placed at intervals across a subject's scalp, reducing thenumber of electrodes in array 20 may allow array 20 to be positioned ona subject's forehead, thereby eliminating the need to place electrodesover the subject's hair. This may reduce any conduction problems causedby hair and eliminate the need for hair removal. Apparatus 10 may beconfigured to compensate for the reduced number of electrodes in array20 by employing signal processing algorithms capable of accommodatingfor the missing electrodes. Such processing may be performed byprocessor 51 in base unit 42 or by external processor 48. Although notshown, a processor may be placed on array 20 itself, facilitating datagathering and transmission, or the data processing described herein.Adapting apparatus 10 to work with array 20 having fewer electrodes mayallow for quicker placement of the electrodes on a subject, which may inturn facilitate efficient subject monitoring and point-of-care use.

In accordance with the embodiments depicted in FIGS. 2A and 2B,electrodes Fp1, Fp2, F7, F8, AFz, FPz, A1, and A2, as known from theInternational 10/20 system, may be placed on the right ear lobe atposition 302, on the far right of the forehead at position 304, on thenear right of the forehead at position 306, on the center top of theforehead at position 308, on the near left of the forehead at position310, on the far left of the forehead at position 312, and on the leftear lobe at position 314. Additionally, in an illustrative embodiment, agrounded electrode may be placed on the center of the forehead atposition 318.

Though a general desired arrangement of electrodes on the forehead maybe known, achieving consistent placement of electrodes across subjectsin locations capable of generating usable signals from each electrodehas proven very difficult. Individually placing, testing, and adjustingeach electrode on a subject using free electrodes may yield the best EEGsignals, but individual placement requires more time and a trainedtechnician, as discussed above. This would negate the ease-of-use andportability requirements for a point-of-care embodiment of apparatus 10.Prior art “one-size-fits-all” headsets were created to enable rapid andrepeated placement of electrodes on a subject. Electrode nets weredesigned that adjust in proportion to the size of a subject's head.Thus, though the relative location of the electrodes to one another wasnot fixed, the electrodes were automatically placed according to thecharacteristics of the net structure, e.g., the rigidity or elasticityof the net, as it conformed to the subject's head. Such nets did notallow for adjustment of the electrodes once the nets were fitted inplace. In addition, headsets were produced that fixed the location ofthe electrodes relative to each other within the headset, so that whenthe headset was applied to the subject, the headset dictated thearrangement of the electrodes on the subject's head. These prior artheadsets were configured to fit on each subject in substantially thesame orientation in an attempt to minimize the risk that an untraineduser would not achieve consistent placement of the electrodes. By fixingthe location of the electrodes relative to each other, affixing theheadset as a unitary whole to the subject essentially simultaneouslycompleted placement of the electrodes, because the headset substratesubstantially determined the relative arrangement of the electrodeswithin it. Thus, the headset itself almost completely dictated theplacement of the electrodes rather than the user, notwithstandingdifferences in facial morphology between subjects.

This fixed-electrode design may generate usable EEG signals in somecontexts. For example, headsets with fixed electrode placement have insome instances been used to measure the sedation level of subjectsundergoing anesthesia. In this context, the fixed electrode headset maygenerate EEG signals that are usable to compare and distinguish betweena subject's alert levels of electrical brain activity and electricalbrain activity indicative of various levels of sedation within thatsubject. Surprisingly, however, headsets that uniformly fix theplacement of electrodes may produce insufficient EEG signals that areincapable of reliably comparing and distinguishing between levels ofnormal versus abnormal electrical brain activity for an individualsubject relative to a population. While not being bound to the theory,this may occur because changes in EEG signals may be more substantialwhen anesthetizing a subject, but the changes in EEG indicative of brainabnormalities in a subject may be more subtle. Thus, the adverseconsequences of fixed-headset designs may be more apparent in moresubtle applications, rendering the fixed headsets unusable.

Although fixed-electrode headsets may ensure the ‘correct’ relativepositioning of electrodes as defined by the headset, the subject EEGreadings provided by these electrodes surprisingly are not actuallyusable for all applications, which may be unexpected to one of skill inthe art. Further, adjusting the headset to accommodate the anatomy ofdifferent subjects (e.g., moving the headset to avoid the hair line orother anatomical feature) or offering different sizes of fixed electrodeheadsets (e.g., youth or adult) did not appear to achieve more usableEEG readings. Thus, the problem of providing an easy-to-apply set ofelectrodes for a point-of-care neuro-assessment apparatus remained, anda need persisted for a headset and method for accurately and efficientlyapplying electrodes to a subject.

According to an embodiment of the present disclosure, FIG. 3 depicts anelectrode array 400 configured to solve at least some of the aboveproblems. Array 400 includes a substrate 401; right and left ear lobeelectrodes 402, 414; far right and far left forehead electrodes 404,412; near right and near left forehead electrodes 406, 410; center topforehead electrode 408; and grounded center electrode 418. Thoughgrounded electrode 418 is shown in the lower center of array 400,electrode 418 may be located in any suitable position on array 400. Insome embodiments, including the one shown in FIG. 3, array 400 mayinclude two bilateral “branches” (e.g., extensions left and right of acenterline corresponding approximately with the nose), each configuredto extend laterally along respective approximate halves of a subject'sforehead region. The electrodes may be arranged along the branchingportions of array 400. In the embodiments of FIGS. 3-5, the electrodesmay connect to the branching portions of array 400 via, e.g., connectorregions 430. While some of the electrodes may be attached directly toneighboring electrodes in array 400 (e.g., central electrode 408 andground electrode 418), some of the electrodes may be independentlyconnected to each branch of array 400 and, for example, may extend fromthe branching portions of headset 400 via separate, individualconnections. The array 400 depicted in FIG. 3 is bilaterallysymmetrical, with the connector region 450 aligning approximately withthe nasal centerline, but this needn't be the case.

Array 400 may be sized and shaped to conform to a subject's forehead.Array 400 may be configured to extend from an ear region of the subjectand across the forehead, and may include securing devices 424, such asear loops, to fit over a subject's ears and hold array 400 in place.Further, ear loops 424 may position electrodes 402 and 414 on asubject's ear lobes. Though ear loops 424 are depicted as maintainingarray 400 in place, any suitable mechanism, for example, bands, straps,adhesives, snaps, Velcro® or clamps, either completely or partiallyencircling or affixing array 400 to the head, may be used in addition toor instead of ear loops 424 to maintain array 400 in place. Further,although a branching configuration is described in the exemplaryembodiment, array 400 may have any suitable shape, size andconfiguration.

The electrodes may be incorporated into array 400 on the side of array400 configured for contacting the subject. The portion of the electrodesconfigured for subject contact may be exposed and may either lie flushwith array 400 or may slightly recess into or project from array 400. Toprotect the electrodes prior to use, the exposed surfaces may becovered, for example with a removable cover or covers, until array 400is applied to a subject. Further, array 400 may also include a wet ordry gel over the electrodes and protected by the cover to aid inelectrode placement. Alternatively, gel may be applied to the subject orto the electrode directly before use. In some embodiments, theelectrodes (with the possible exception of electrodes 402, 414) may bespatially arranged in array 400 to reflect the approximate 10% and 20%distance away from a center nasion tab 420 (discussed further below),according to the International 10/20 system, as estimated for the headsize of an average subject.

Array 400 may include circuitry embedded into or printed, coated,etched, deposited or bonded onto array 400 to operate in conjunctionwith the electrodes. The circuitry may be composed of any suitableelectrically conductive material, such as, for example, copper, silver,silver-chloride, gold, tin, or any combination of materials known in theart. The circuitry may electrically connect each electrode, eitherindividually or jointly, to connector region 450 and/or to a transmittercapable of relaying the detected electrical brain activity data from theelectrodes to base 42 or external processor 48. Array 400 may include abase interface region 450 configured to connect with base 42, eitherwirelessly or through a hard connection. Though interface region 450 isdepicted at the center of array 400 and array 400 is depicted assymmetrical, base interface region may be any suitable size and shapeand may be positioned anywhere on array 400. Further, in wirelessembodiments, base interface region may include a transmitter fortransmitting data, or may be entirely missing from array 400.

Unlike previous electrode headsets, array 400 may be configured toachieve accurate application of electrodes by an untrained person whilegenerating usable EEG readings for assessing normal versus abnormalbrain function. Array 400 will be further described below in referenceto the application of array 400 to the subject.

Array 400 may be applied to the forehead of a subject with ear loops 424disposed around a subject's ears, as depicted in FIG. 4A, generallypositioning array 400 across the subject's forehead and maintainingarray 400 in place. Once array 400 is preliminarily in place, as isdepicted in FIG. 4B, a nasion point 420 on headset 400 may be alignedwith the subject's nasion region, located at the top of the nose in adepressed region directly between the subject's eyes. Positioning nasionpoint 420 so that the lower tip aligns with the patient's nasion maysubstantially align the front, center portion of array 400 on thesubject. Next, the position of center electrode 408 may be checked andadjusted if necessary. If positioning the tip of nasion point 420directly at the subject's nasion causes electrode 408 to fall within thesubject's hairline, then electrode 408 and array 400 may be lowered onthe subject's forehead so that electrode 408 is located just below thehairline. This allows electrode 408 to be positioned on the skin of theforehead rather than in the hair, reducing the interference that may becreated by positioning the electrode over the hair. This may allow array400 to be adjusted for the unique anatomical features of the subject.Positioning nasion point 420 and center electrode 408 may occur eitherbefore or after arranging ear loops 424 around the subject's ears. Onceear loops 424 are positioned over the ears, electrodes 402 and 414 maybe attached to the subject's ear lobes.

Once electrode 408 is positioned, electrodes 406 and 410 may requireadjusting. The position of electrodes 406 and 410 may be adjustedrelative to the subject's supraorbital foramen, which is located abovethe eye socket where the subject's eyebrows are located. For the purposeof this application, the words ‘eyebrow’ and ‘supraorbital foramen’ maybe used interchangeably. To allow the person applying array 400 toposition electrodes 406 and 410 on a subject, array 400 may include oneor more distance indication gauges. In FIG. 4A through FIG. 5, thedepicted distance indication gauge includes tabs 422 extending down fromelectrodes 406 and 410. The distance from the bottom tips of tabs 422 tothe center of electrodes 406 and 410 corresponds to the optimalpredetermined distance between electrodes 406 and 410 and the top of thesubject's eyebrows. Tabs 422 are positioned on the subject so that thebottom of tabs 422 sits above, preferably directly above, the peak ofthe subject's eyebrow so that the bottom of tabs 422 does not touch thesubject's eyebrows. If the subject does not have any eyebrows, then thebottom of tabs 422 is positioned above the peak of the subject'ssupraorbital foramen, which lies in substantially the same location asthe eyebrows.

Positioning tabs 422 directly above the subject's eyebrows may locateelectrodes 406 and 410 in an optimal location for recording usable EEGreadings from the subject using array 400. Prior electrode arrays andheadsets focused predominantly on the positioning of each electroderelative to each other and attempted to provide a way to maintainuniform positioning of the electrodes relative to each other for eachsubject. Accordingly, in such devices, electrodes 406, 410, and 408 hadfixed, non-adjustable positions in the headset and were applied alltogether to a subject. Thus, the position of electrodes 406 and 410relative to center electrode 408 could not be adjusted. While this fixedarrangement worked for some uses, as discussed above in reference tosedation-monitoring purposes, this fixed arrangement of electrodes 406,410, and 408 unexpectedly provided inadequate EEG readings fordiscriminating between normal and abnormal electrical brain activityindicative of normal or abnormal brain function. For example, FIGS. 6Athrough 6C show data from experiments that measured and compared severalexemplary properties of EEG signals recorded using free electrodes, afixed headset, and an adjustable headset according to an exemplaryembodiment of the disclosure. The graphs of FIGS. 6A through 6C depict12 frontal features that were extracted from the EEG readings of normalsubjects and the mean statistical z-score value of each featurecalculated for all subjects tested in each of the free electrode, thefixed headset, and the adjustable headset groups. Thus, the meanz-scores of each feature are compared using the different EEG recordingdevices.

Features 1 through 12 shown in FIGS. 6A through 6C were achieved bycalculating the bipolar absolute power for a pair of electrodes for eachheadset type within selected frequency bands, (a left and right featureacross 6 frequency bands for a total of 12 features), and the phasesymmetry and coherence relationships among these spectral measurementswithin and between pairs of electrodes. Measurements may be made betweenpairs of electrodes in a given headset in order to detect signaldifferences and to reject input signals common to both electrodes. Thisis because each electrode may acquire different brain activity, butnoise influence may be similar on both electrode channels within thepair due to their close proximity on the subject's forehead. Thecomputed measures were combined into a single measure of EEG signal perchannel and transformed for Gaussianity, and a statistical ztransformation was performed to produce z-scores. The z-transform wasused to describe the deviations from normal EEG values.

The z-scores were calculated using a database of response signals from alarge population of subjects believed to be normal. Thus, the z-scoreswere used to calculate the probability that the extracted featureobserved in a subject conformed to a normal value. In the exemplary dataof FIGS. 6A through 6C, a mean value of any feature for a “more normal”population would lie closer to the mean value for the normativepopulation (i.e. mean=0, standard deviation=1) than the mean values ofany feature in the “less normal” population. FIGS. 6A through 6C depictEEG measurements from normal subjects, thus the z-scores would beexpected to lie closer to 0, with some normal variation. As the datashows, the mean z-score values for the fixed headset and the adjustableheadset varied greatly, while the z-score values of the adjustableheadset and the free electrodes more closely resembled each other andgenerally lie closer to a mean of 0. While the sample sizes for thefixed and adjustable headset groups were smaller than the sample sizeused for the free electrode group (which may explain why both of thesegroups displayed z-scores further from 0), the z-scores of the fixedheadset group were noticeably different than the adjustable headsetgroup across the exemplary set of features.

FIG. 6A compares features from bipolar absolute power measurementsrecorded with fixed and adjustable headset designs and free electrodes.Bipolar absolute power indicates the amount of energy being acquired bythe electrodes. This property should be substantially consistent acrossthe headset designs, as each headset should in theory be measuringsimilar brain electrical activity. FIG. 6A shows that the amount ofenergy detected by the fixed headset was substantially greater than thatof free electrodes, which may imply that the fixed headset detected morethan simply the EEG signal. Such noise may have been caused, e.g., bymuscle activity due to placement of the electrodes near the eyebrows.

FIG. 6B compares features from coherence measurements recorded acrossthe various electrode placement techniques. Coherence indicates thesimilarity of frequency content between the detected EEG signals. A morenegative coherence value implies that the acquired EEG signalfrequencies are less correlated, while a more positive value impliesthat detected signal frequencies detected are more correlated. Onceagain, across each feature, free electrodes and the adjustable headsetdisplayed substantially similar coherence values, and, on average, thesecoherence values were noticeably different from those of the fixedheadset. The more negative coherence values acquired by the fixedheadset indicate that the detected signals are less correlated than theyshould be, which may again indicate signal contamination.

FIG. 6C compares features from phase synchrony measurements recordedwith each electrode placement technique. Phase synchrony is similar tocoherence, but includes measurement of the phase relationship betweenthe pair of electrodes recorded. Thus, this feature analysis indicatesthat EEG recordings measured with the fixed headset were not only of adifferent frequency than expected, but also that these frequencies werenot in phase. By contrast, recordings of the exemplary features takenwith the free electrodes and the adjustable headset generally displayedmore similar phase synchronies.

As the inventors' data illustrates, the EEG readings detected usingarray 400 are substantially different from those of fixed headsets,which marked a surprising discovery. It was previously believed thatelectrodes 406 and 410 should be located a set distance from centerelectrode 408. Thus, previous, fixed-headset devices reflected theconcern that placing electrodes 406 and 410 too close to centerelectrode 408 would cause electrical shunting, increasing the noise anddecreasing the amplitude of any detected EEG signals. Thus, previousheadsets were designed to fix the distance between these electrodes, andthe entire block of electrodes, as well as the grounding electrode, wereapplied in a predetermined, uniform position to a subject. Only theblock of electrodes could be repositioned slightly on the subject; theelectrodes could not be individually adjusted relative to each other.Yet, this approach produced EEG readings that did not accurately allowfor detection of normal versus abnormal brain activity, as discussedabove.

By contrast, as a result of much experimentation, the disclosed arrayshifts away from this fixed design and reflects the surprising discoverythat achieving usable EEG readings involves a compromise between theproximity of electrodes 406 and 410 to electrode 408 and the proximityof electrodes 406 and 410 to the supraorbital foramen. Electrodes placedin the eyebrows of a subject may induce unwanted physiological effectson recorded EEG data, such as undesirable noise. The human face containsa number of muscles to control the movement of the eyes and eyebrows.Positioning electrodes 406 and 410 too close to the eyebrows may causeinterference from the electrical activity of these muscles. By contrast,the forehead contains fewer muscles, and so positioning electrodes 406and 410 away from the eyebrows by a set distance may result in clearer,more accurate, and more usable signals, as long as electrodes 406 and410 are not placed too close to electrode 408.

After gathering much experimental data, it was discovered that there maybe a calculable, average distance above a subject's eyebrows that maycorrelate to an optimum electrode position for generating signals usableto determine normal versus abnormal brain activity. When collecting andanalyzing data, the preferred International 10/20 system location wasused to determine ‘ideal’ placement of the Fp1 and Fp2 electrodes(electrodes 406 and 410 in array 400). The 10/20 electrode location is asubject-specific measurement that is determined based on the head sizeof each subject. Accordingly, the ‘ideal’ 10/20 location varies fromsubject-to-subject and must be calculated on an individual basis. Todetermine the average ‘ideal’ electrode placement across a population,head measurements were recorded from a group of subjects and averaged tocalculate where the 10/20 location of the Fp1 and Fp2 electrodes shouldbe relative to the average position of eyebrows and the average headsize of the subjects.

FIG. 7 graphically depicts the relationship between the calculated 10/20location of the Fp1 and Fp2 electrodes based on the measurednasion-to-inion distance in 20 subjects and the distance of thislocation from the top of a subject's eyebrows. As is demonstrated inFIG. 7, with the exception of a few outliers, the ideal electrodeplacement for Fp1 and Fp2 for most subjects tends to fall within anidentifiable range, indicated in FIG. 7 by dashed lines. This rangecorresponds to between approximately 12 millimeters and 24 millimetersabove a subject's eyebrow.

Array 400 may be configured to reflect the discovery that placingelectrodes 406 and 410 a predetermined, consistent distance away fromthe subject's eyebrows may achieve an optimum placement for electrodes406 and 410 to generate reliable EEG readings that are usable fordetermining levels of abnormal versus normal electrical brain function.For example, in some exemplary embodiments, the predetermined distancefrom the eyebrows to the center of electrodes 406 and 410 may equalapproximately 17.7 millimeters. As is demonstrated by the solid line inFIG. 7, for the average person, centering the Fp1 and Fp2 electrodes17.7 millimeters above the eyebrow may achieve the average optimalelectrode placement across a population of subjects. In someembodiments, the predetermined distance used may vary, and theelectrodes may be positioned slightly closer to or slightly farther fromthe eyebrow. As is demonstrated by the dotted lines in FIG. 7,positioning the Fp1 and Fp2 electrodes between approximately 12millimeters and 24 millimeters may achieve an optimum placement. Inaddition, the electrodes may be sized so that when the center of theelectrodes are placed 17.7 millimeters above the eyebrows, the size ofthe electrode itself spans a portion or substantially all of this range.Further, this range may change for given populations. For example, array400 may be designed for youths and may position electrodes 406 and 410closer to the eyebrows to reflect a smaller average head size. In someembodiments, array 400 may be designed for a population of professionalathletes, e.g., football, soccer, or hockey players, and the electrodesmay be positioned farther from the eyebrows to reflect a larger averagehead size. Accordingly, measurements from a specialized sub-populationmay be taken to create a specialized array 400. In some embodiments, thepredetermined average distance may also vary depending on theconfiguration of array 400 used, including, e.g., the size of theelectrodes or the configuration of substrate 401.

Once the predetermined distance is calculated, the distance indicationgauge of array 400 may be formed to achieve this predetermined distance.Based on the size and location of the electrodes and the size and shapeof substrate 401 depicted in the exemplary array 400 of FIGS. 3 through5, the length of tabs 422 may be approximately 5 millimeters in lengthin order to position electrodes 406 and 410 a predetermined distance ofapproximately 17.7 millimeters away from a subject's eyebrows. One willappreciate that the length of tabs 422 may vary in order to achieve thepredetermined distance depending on the placement of electrodes withinarray 400, the size and shape of substrate 401, or any other variationsin configuration of array 400 and/or the calculated predetermineddistance. For example, if substrate 401 extends further in a distaldirection below electrodes 406 and 410, then tabs 422 may be shortenedto achieve the same predetermined distance from the bottom of tabs 422to the center of the electrodes.

As can be seen in FIGS. 3-5, electrodes 410 and 406 are not directlylaterally tethered to electrode 408 and grounded electrode 418 by array400, allowing the electrodes to be applied to a subject independently ofone another. Decoupling electrodes 406, 410, and 408 may also have thebenefit of reducing muscle-induced interaction that may otherwise occurbetween the electrodes. Yet, removing the fixed arrangement ofelectrodes once again decreases the likelihood that a lay person at thepoint-of-care would be able to effectively apply array 400 to thesubject. Thus, array 400 may be configured to dictate to the user whatadjustments should be made and how to accomplish them.

Incorporating tabs 422 into array 400 allows an untrained person torapidly and accurately place electrodes 406 and 410 onto a subjectproperly for signal acquisition. Ready visual confirmation that tabs 422do not rest at the top of the subject's eyebrows once electrode 408 isin place can be quickly remedied by manual adjustment of the placementof electrodes 406 and 410. As is shown in FIG. 4B, when array 400 isfirst placed on a subject, tabs 422 may extend beyond the top of thesubject's eyebrows once electrode 408 is set in place below thesubject's hair line. This suboptimal placement could compromise signalquality, and ultimately reliability of calculated results. FIG. 4C showselectrodes 406 and 410 adjusted so that the bottom of gauge tabs 422 arealigned in a prescribed way, which for the purposes of this example, iswith the tip of the tabs 422 just above the eyebrow. Of course, otherindicia of alignment may be employed without limitation.

As is shown in FIG. 4C, electrodes 406 and 410 may be connected to array400 via connector regions 430. Connector regions 430 may be flexible andmay allow electrodes 406 and 410 to be moved upwards towards electrode408 so that connector regions 430 bow out, as is shown in FIG. 4C. Insome embodiments, connector regions 430 may be retractable into thebranching portions of array 400, or may be otherwise folded orconfigured to allow at least vertical movement of electrodes 406 and410. Thus, a user may adjust the relative spacing of electrodes on array400 by moving electrodes 406 and 410 so that the bottom of tabs 422 restabove the subject's eyebrows, as discussed above.

Incorporating distance indication gauges, such as tabs 422, into array400 may promote consistent headset orientation and application whileachieving the adaptability required to obtain usable EEG readings, basedon the recognition by the present inventors of the relationship betweensignal quality and the distance between the supraorbital foramen andelectrodes 406 and 410, and the further recognition that while relativeelectrode placement laterally can vary with facial morphology, thisdistance is substantially stable among subjects. While the exemplaryembodiments depict distance indication gauges in the form of tabs 422,any suitable distance indication gauge, indicia, device, or combinationsthereof may be included in array 400. For example, the portions of array400 containing electrodes 406 and 410 could themselves be sized andshaped so that the distance between the bottom of the these portions andthe electrodes reflects the ideal distance from the supraorbitalforamen. In such embodiments, array 400 may not include tabs 422, andinstead, the portions of array 400 around electrodes 406 and 410 maysimply extend down to where the bottom of tabs 422 is shown in FIGS.3-5. Thus, rather than aligning tabs 422, a user applying array 400 maysimply adjust 406 and 410 so that the bottom of each rests directlyabove the eyebrow. In such embodiments, portions 406 and 410 containingthe electrodes may be elongated, oval, rectangular, triangular, or anyother suitable shape.

In some embodiments, a distance indication gauge for array 400 mayinclude one or more sensors configured to detect when ideal electrodeplacement has been achieved. For example, the area of array 400 aroundelectrodes 406 and 410 may include sensors to detect whether theelectrode is positioned too close to the muscles underlying the eyebrowregion. Such sensors may, e.g., emit a wavelength of light and measureone or more properties of a reflected light wavelength to determinewhether the electrode is located too close to muscles to avoid theintroduction of unwanted noise into subsequently recorded signals.Similar sensors may be included in other electrodes, e.g., 404 and 412,to indicate whether an electrode is being placed too close to anunderlying artery, vein, or other anatomical structure. In someembodiments, electrodes 406 and 410 and base 42 may be configured sothat if electrical brain activity outside of a given range is recorded,a user may be prompted to check the placement of these, or any other,electrodes. Such distance indication gauges are purely exemplary, andarray 400 may include any suitable type of distance indication gauge forany indicating preferable placement of any electrode, or any combinationthereof.

Once electrodes 406 and 410 have been positioned on the subject,electrodes 404 and 412 may be attached to the outer forehead region.Once array 400 is in place on the subject and each of the electrodes hasbeen attached to the subject, array 400 may be operably coupled, eitherthrough a direct connection or wirelessly, to base 42, and EEG readingsmay be commenced. For example, in the embodiment depicted in FIG. 3,array 400 may include a base interface region 450 configured to couplewith a suitable connection device attached to base 42.

Thus, a method of attaching array 400 to a subject may includepositioning tab 420 at the nasion region of the subject to alignelectrodes 418 and 408, then adjusting the location of electrode 408 sothat electrode 408 sits on the forehead directly below the hairline, andattaching electrodes 408 and 418 to the forehead. The method may furtherinclude engaging ear loops 424 with the ears of the subject so thatarray 400 is positioned across the forehead, and attaching electrodes402 and 414 to the ear lobes of the subject. In some embodiments, thesefirst two steps may be performed in reverse order, and electrodes 402and 414 may be attached at any point during application. Next,electrodes 406 and 410 may be positioned by aligning tabs 422 directlyabove the eyebrows of the subject, so that the bottoms of tabs 422 donot touch the eyebrows of the subject. Electrodes 406 and 410 may thenbe attached to the subject. Electrodes 404 and 412 may then be attachedto the forehead of the subject.

The electrodes of array 400 may be attached to the subject in anysuitable manner. The electrodes included in array 400 may be anysuitable type of electrode, e.g., wet gel or solid gel electrodes, orany combination thereof. The electrodes of array 400 may have backingsor covers that may protect the electrode until being placed on thesubject. A user may uncover the electrode prior to attaching theelectrode to the subject. Any suitable backings may be used, such asremovable, tear-able, or peel-able backings with or without an adhesive.In some embodiments, electrodes with, e.g., adhesive-free peel backings,may be used that allow for repositioning of the electrode on a subject.For example, a user applying headset 400 may accidently attach theelectrode in the wrong place, such as accidently placing electrode 406or 410 into, or at the wrong distance from, the eyebrow of a subject.This repositioning feature is desirable in urgent care or battlefieldconditions, where placement of array 400 might take place in stressfulor distracting situations. Additionally, an electrode site revealed ashaving a high impedance value when recording EEG signals may require theelectrode to be removed, the skin re-prepped, and the electrodere-attached. In such instances, the user may need to adjust theplacement of the electrode on the subject. In such an embodiment, tabs422 may aid in repositioning. For example, a user may lift tab 422 topull the corresponding electrode off of the subject's skin whileallowing the user to avoid touching any adhesive, gel, or the electrode,so as to preserve usability of the electrode. In this manner, tabs 422may serve a secondary function of aiding in the repositioning ofelectrodes on the subject, if necessary. This is another desirablefeature in a battlefield or urgent-care setting, where the skin surfacemight be contaminated with dried blood, or the subject may exhibitindividual features such as facial scarring, wrinkling, eczema,dermatitis, etc. Further, tabs 422 may also enable a user to more easilyremove the electrodes and array 400 from the subject after completion ofthe EEG testing. To this end, other electrodes, such as electrodes 404and 412, e.g., may include one or more tabs to achieve these secondaryfunctions of repositioning and removal of the electrodes.

Accordingly, array 400 may be configured to allow multi-axis,independent control over the placement of individual electrodes. Tofurther aid with the multi-axis adjustability of array 400, array 400may also include visual indicia indicators on array 400 to instruct theuser in proper alignment and use of array 400. For example, as is shownin FIG. 5, array 400 may include graphical indicators, text, or othersymbols to indicate the preferred placement of array 400 on a subject.For example, nasion point 420 and tabs 422 may include arrows 610 and602, or other suitable symbols, indicating where these components ofarray 400 may be positioned by the user. In some embodiments, portionsof array 400 may include illustrations 606 pictorially demonstrating toa user where on the anatomy of a subject a given electrode may beplaced. Further, indicators 604 may be included and may mark theposition of the underlying electrode, e.g., the center or the edge ofthe electrode, to aid positioning. In the embodiment shown in FIG. 5,indicators 604 are used in combination with illustrations 606 totogether demonstrate to a user where to place the underlying electrodeon a subject. Further, textual indicators may be included on array 400.For example, in FIG. 5 nasion point 420 includes instructions to alignthe nasion point first, and electrodes 406, 410 may include textinstructing a user to place tab 422 above the eyebrow. Additionally,textual indicators may warn to avoid other anatomical features, e.g.,electrodes 404, 412, and 408 may wam a user to avoid placing theelectrodes over an artery, muscles, or hair, for example. In someembodiments, one or more electrodes may include electrode labels to aida user in distinguishing the electrodes from one another and forreference, e.g., in a set of instructions. In some embodiments, text orgraphics may be incorporated that convey to the user the order in whichelectrodes should be placed or may include instructions for performingEEG recordings. Any suitable number, arrangement, or type of visualindicators may be included, including, e.g., color coding or shading. Insome embodiments, visual indicators may change, for example, to signalto a user that an electrode is or is not correctly in place. In someembodiments, e.g., array 400 may include one or more lights that changecolor to indicate that a sensor is or is not correctly in place, e.g.,by performing a preliminary impedance check. Further, any suitablenon-visual indicators may be used, for example tactile (e.g., texture)or auditory indicators.

Referring back to FIG. 1, the memory 52 of brain-state assessment device10 may contain interactive instructions for placing and adjusting array400 and operating the device, which may be displayed, e.g., on thescreen of user interface 46 or output from a speaker (not shown).Instructions may include, e.g., audio and/or visual instructions foroperating the device, such as text or graphics displayed on the screento illustrate instructions for placing and attaching array 400 and/oroperating and using the device. These instructions may refer to one ormore of the visual indications on array 400, if such indications areincluded. The inclusion of interactive instructions with the device mayalso promote point-of-care deployment and use of apparatus 10 by personsother than medical professionals.

In some embodiments, once array 400 has been applied to a subject andconnected (either physically or wirelessly) to base unit 42, base unit42 may be configured to aid a user in determining whether suitableplacement of array 400 has been achieved. For example, base unit 42 mayrun a preliminary impedance check to determine whether array 400 isready to begin recording and testing or whether additional modificationsto array 400 on the subject are necessary. In some embodiments, oncearray 400 is positioned on the subject and connected to base unit 42,the user may employ user interface 46 to initiate a pre-test sequence,or a pre-test sequence may be initiated automatically. During a pre-testsequence, impedance may be automatically measured on each electrodechannel, either simultaneously, individually, or in groups, by sending asmall amplitude sinusoidal signal to the electrodes via groundedelectrode 418. The resulting current, which is proportional toimpedance, may then be measured for each electrode.

Base unit 42 may then output data regarding the status of each electrodeto the user. For example, a display in base 42 may indicate the currentand/or impedance value measured for each electrode and may indicatewhether the measured value falls within an normal range for thatelectrode. This may be accomplished using visual output (e.g., text orgraphics), auditory output, or a combination thereof. For example, adisplay in user interface 46 may depict a diagram of each electrode onthe subject and the corresponding measured impedance value for each. Theexpected impedance range and/or whether an electrode falls in theexpected range may also be depicted. These values may either be depictedusing text or graphics or a combination. In some embodiments, theelectrodes may be color-coded according to the measured impedance ofeach to indicate whether the recorded value is within an optimal rangeor not. For example, green may indicate that an electrode has a normalimpedance value, yellow may indicate an acceptable impedance value, andorange may indicate an unacceptable impedance value. A normal impedancevalue may be identified as between approximately 0.5 and 5.0 kΩ, anacceptable impedance value may be between approximately 5.0 and 10.0 kΩ,and an unacceptable impedance value may be greater than approximately10.0 kΩ.

Based on this information, a user may adjust one or more electrodesbefore initiating testing. Tabs 422 may assist with the adjustment ofone or more electrodes, as discussed above. Adjusting may includelifting the problem electrode, re-prepping the underlying area on asubject, and re-attaching the electrode. Once the electrodes areadjusted, this pre-check sequence may be performed again. Once normaland/or acceptable values are achieved for each electrode in array 400,testing may begin either automatically or via user input. In someembodiments, apparatus 10 may not allow testing to begin until base 42detects that all of the electrodes have impedance values falling withina predetermined range.

In some exemplary embodiments, array 400 may be applied to a subject,base 42 may be powered on, and a user may indicate that a new test willbe performed. At this step, patient information (such as date of birth,name, patient ID number, sex, age, physiological parameters, etc.) orarray 400 information (such as model number, lot number, calibrationinformation, etc.) may be entered using user interface 46. At thispoint, an impedance pre-check screen may be selected or mayautomatically appear, and an impedance check as described above may beinitiated.

In some embodiments, placement of array 400 on a subject and connectionof array 400 to base 42 may initiate other communications between array400 and base 42, instead of, or in addition to, an impedance check. Forexample, connecting array 400 may prompt base 42 to power on or maycause base 42 to receive and/or relay information about array 400, e.g.,its expiration date, model number, lot number, calibration information,the number of times array 400 has been used, or any other suitableinformation or combination of information. Such information may promoteproper use of and/or accurate readings from system 10.

Array 400 may be disposable or reusable. In some embodiments, theelectrodes of array 400 may be mounted on a low-cost, disposableplatform. Array 400 may be formed of any suitable flexible or rigidmaterials, including, e.g., plastic, foam, rubber, silicone, or anycombination thereof. In some embodiments, array 400 may be formed ofmultiple layers, for example, portions of array 400 may includereinforcement layers to provide structural stability, dielectric layers,or adhesive layers for maintaining array 400 on a subject. For example,ear loops 424 may include an additional layer of foam or padding forstability or to increase subject comfort. Ear loops 424 may also includea malleable, internal layer or wire to allow an operator to bend the earloops around a subject's ears, providing improved anchoring of array 400on a wider range of head shapes and sizes. Further, any circuitry onarray 400 may be covered by a dielectric layer to help insulate orprotect the circuitry, which may be formed of, e.g., polyamide,polyester, aramid, or any dielectric or combination thereof. Such layersmay extend across the entire array 400 or may extend across only aportion of array 400. In multi-layer embodiments, the layers of array400 may be attached in any suitable manner, e.g., bonding, adhesives,mechanical fasteners, or any combination thereof.

In some embodiments, array 400 may be configured to adjust to any numberof subject head sizes or geometries. For example, array 400 may includeadjustable bands, straps or loops, or may stretch or include anysuitable mechanism for conforming to a range of subject head sizes andanatomical variations. In some embodiments, array 400 may include one ormore expansible regions, for example, outward-bowing humps oraccordion-shaped articulation ridges, capable of flattening to expand orcontracting to adjust to a subject's head shape and/or size. Suchregions may include flexures, elastics, corrugations, serpentinegeometries, or any other suitable construction to allow variation inoverall size, e.g., height or length, of array 400. For example,securing ear loops 424 to the ears of a subject and positioning array400 across the forehead may cause any expansible regions to stretch orcontract to accommodate the head geometry and size of the subject.Additionally, by permitting independent placement of the electrodes,array 400 may further be able to accommodate an increased range ofsubject sizes and anatomies. Further, array 400 may also come indifferent sizes, e.g., for youths or adults. In some embodiments, array400 may be configured for easy and/or rapid placement on a subject.

Surprisingly, when testing prior headset designs, it was discovered thatthe bulk and design of the array itself may also affect EEG readings,beyond just determining or influencing the spacing and arrangement ofelectrodes. For example, when free electrodes were applied to a subjectand then the space between the electrodes on the subject's skin wasfilled in and covered with an inert material (e.g., tape, paper, orfoam), the EEG readings received from the headset in some instances wereless useful for discriminating between levels of normal and abnormalbrain activity for diagnosing disease or injury and more closelyresembled the readings from the fixed headset designs. Without beingbound by theory, the present inventors speculate that this phenomenonmay be because the placement of more material into contact with asubject's forehead may induce electrical activity, for example, bymuscular twitching or by the activation of sensory neurons responsive totouch. This electrical activity in turn may introduce noise into the EEGsignals. Accordingly, some embodiments of the present disclosure mayinclude arrays 400 that are configured to reduce the amount of materialin contact with the subject, as well as to allow for adjustability ofelectrodes. For example, portions of array 400 may be streamlined orhave geometries configured to decrease contact between array 400 and thesubject. For example, portions of array 400 that are configured to flexor extend to fit various head sizes or to allow for adjustment ofindividual electrodes may be configured to bow away from the subjectwhen flexed, so as to decrease contact between the subject and theheadset. Decreased contact and/or streamlined configurations may havethe added benefit of allowing a user placing array 400 on a subject tosee more of the subject's forehead when placing array 400 on the subjectand when adjusting and attaching electrodes 406 and 410, which maypromote quick application of array 400. Thus, different embodiments ofthe disclosure may be configured to offer different degrees of contactbetween array 400 and the subject and may have different widths, forexample, of the branching portions of array 400 or connector regions430.

Referring back to FIG. 1, the electrodes in array 400 may be configuredto measure the electrical fields that are produced as a result of asubject's electrical brain activity. The activity may be spontaneous,evoked or a combination thereof. In some embodiments, spontaneous brainactivity may be measured while a subject is at rest or while thesubject's eyes are closed, to reduce the number of stimuli the subjectis exposed to during the testing (i.e., remove visual stimuli). In someembodiments, both spontaneous and evoked responses may be measured. Theevoked response may be obtained by stimulating the subject using visual,physical, aural or other suitable stimulation. In such an embodiment,one or more stimuli may be delivered to the subject via a stimulusdelivery device 31, which may be separate from or incorporated intoarray 400. Stimuli generator 54 in base 42 may relay a signal tostimulus delivery device 31, initiating the delivery of one or morestimuli to a subject to obtain an Auditory Evoked Response (AEP). Insome embodiments, array 400 may also include sensors in addition to theelectrodes discussed above, for example, to measure the heart rate,temperature, blood pressure, or other suitable physiological parametersof the patient to relay to base 42. Such additional information may bemonitored, either continuously or intermittently, and/or used inaddition to the EEG readings to assess brain function and subjectcondition.

Functional brain state assessment may be made by recording and analyzingelectrical brain activity of subjects with suspected neurologicalinjury. A handheld, easy-to-administer brain wave assessment device mayfacilitate neurological evaluation of subjects at the point-of-care,which in turn may allow rapid and accurate initiation of therapy. Oncearray 400 is applied to a subject, a subject's brain electrical impulsesdetected by the electrodes may be transmitted to base unit 42 and/or anexternal processor 48 for signal analysis and data processing.Additionally, these components may perform other steps, including signalamplification, artifact rejection, signal extraction, and classificationof signal features. Base 42 and/or external devices may process EEG datausing any combination of signal processing methods, algorithms, andstatistical analysis to extract and/or organize signal features,including, e.g., Fast Fourier Transform (FFT) analysis, waveletanalysis, Linear Discriminant Analysis, spectral analysis, microstateanalysis, fractal mathematics, nonlinear signal processing, anddiffusion geometric analysis, to analyze and classify electrical brainactivity.

Advanced signal processing algorithms may be used in conjunction with adatabase of pre-recorded brain activity received from thousands ofsubjects having different neurological indications to assess theneurological function of a subject, e.g., whether it falls within normalor abnormal ranges, or varying degrees thereof. The dysfunctionsdetected may include, for example, seizure, ischemic stroke, elevatedintracranial pressure, hematoma, concussion/contusion/TBI, dementia, anddepression. The results of such analysis may be displayed to a user onuser interface 46 or communicated to a user in any suitable manner, ortransmitted to or recorded by any suitable end point, e.g., a memory,printer, or emergency response team. Exemplary systems for point-of-careneuro-assessment are disclosed in commonly assigned U.S. PublicationNos. 2011/0144520 and 2012/0065536 and U.S. Pat. Nos. 8,364,254;7,904,144; 7,720,530, which are each incorporated herein by reference intheir entirety. Accordingly, the disclosed electrode array may be usedin conjunction with a portable handheld device for rapid, point-of-care,neurological evaluation to determine an appropriate course of treatmentat an early stage of injury, or other brain disorder requiring medicalattention.

Other embodiments of the disclosure will be apparent to those skilled inthe art from consideration of the specification and practice of thedisclosure herein. It is intended that the specification and examples beconsidered as exemplary only, with a true scope and spirit of theinvention being indicated by the following claims.

What is claimed is:
 1. A headset for detecting brain electrical activityof a human subject comprising: a flexible substrate dimensioned to fit aforehead of the subject having a first end and a second end, wherein thefirst end and the second end each includes a securing device configuredto engage an ear of the subject to position the substrate across theforehead, and wherein the substrate includes at least one expansibleregion permitting a distance between the first end and the second end toselectably vary; a plurality of electrodes disposed on the substrate sothat the electrodes contact the subject when the headset is positionedon the subject; wherein a first electrode is configured to contact a topcenter region of the forehead, a second electrode is configured tocontact a lower center region of the forehead, a third electrode isconfigured to contact a front right region of the forehead, a fourthelectrode is configured to contact a front left region of the forehead,a fifth electrode is configured to contact a right side region of theforehead, and a sixth electrode is configured to contact a left sideregion of the forehead; wherein one electrode is included within eachsecuring device and configured to contact an ear region of the subjectwhen the headset is positioned on the subject, and wherein at least thethird electrode and the fourth electrode are movable in at least avertical direction relative to the other electrodes when the headset ispositioned on the subject; and flexible circuitry in the substrateoperably coupled to each electrode.
 2. The headset of claim 1, whereinat least one of the plurality of electrodes is a grounded electrode. 3.The headset of claim 1, wherein at least the third electrode and thefourth electrode each includes a distance indication gauge.
 4. Theheadset of claim 3, wherein the distance indication gauge includes a tabwith a first end connected to the electrode and a second free endextending from the electrode.
 5. The headset of claim 4, wherein adistance from the second end of the distance indication gauge to acenter of the electrode substantially equals a distance that theelectrode is located from an anatomical feature of the subject when theheadset is positioned on the forehead of the subject.
 6. The headset ofclaim 5, wherein the anatomical feature is an eyebrow.
 7. The headset ofclaim 5, wherein the distance from the second end of the distanceindication gauge to the center of the electrode is substantially equalto 17.7 millimeters.
 8. The headset of claim 1, wherein the at least oneexpansible region includes a flexure or corrugation in the substrate. 9.A method of applying a headset for detecting brain electrical activityto a subject, the method comprising: applying a first sensor to a leftear region of the subject; applying a second sensor a right ear regionof the subject; applying a third sensor to an upper center region of theforehead of the subject; applying a fourth sensor to the forehead of thesubject; applying a fifth sensor to a left frontal region of theforehead of the subject; applying a sixth sensor to a right frontalregion of the forehead of the subject; applying a seventh sensor to aleft side region of a forehead of the subject; applying an eighth sensorto a right side region of the forehead of the subject, wherein theheadset includes a flexible substrate dimensioned to fit the forehead ofthe subject having a first end and a second end, wherein the first endand the second end each includes a securing device configured to engagean ear of the subject to position the flexible substrate across theforehead, wherein the flexible substrate includes at least one distancegauge configured to indicate the distance from an anatomical region ofthe subject from which to apply at least one sensor, and wherein theheadset includes a connector region; and connecting the connector regionto a processor.
 10. The method of claim 9, wherein the connectingincludes wirelessly connecting the connector region to the processor.11. The method of claim 9, wherein the connecting includes physicallyconnecting the connector region to the processor.
 12. The method ofclaim 9, wherein the processor is housed in a portable handheld deviceand is configured to receive data from at least one sensor.
 13. Themethod of claim 12, further comprising: conducting an impedance check,wherein the portable handheld device transmits at least one signal toeach sensor and measures a resulting current from each sensor toidentify an impedance value for each sensor.
 14. The method of claim 13,wherein the portable handheld device includes a display screen fordisplaying the impedance value for each sensor, the method furthercomprising: comparing the identified impedance value for each sensor toa predetermined impedance range to determine whether the impedance valuefalls within the range; and adjusting any sensor that has an impedancevalue that falls outside of the range to cause the impedance value forthat sensor to fall within the range.
 15. The method of claim 9, whereinthe substrate includes at least one expansible region permitting adistance between the first end and the second end to selectably vary.16. The method of claim 9, wherein the fourth sensor is applied to alower center region of the forehead of the subject and the fourth sensoris grounded.
 17. The method of claim 9, wherein the anatomical region ofthe subject is an eyebrow.
 18. The method of claim 17, wherein a firstdistance gauge includes a tab extending from a lower region of the fifthsensor and a second distance gauge includes a tab extending from a lowerregion of the sixth sensor.
 19. The method of claim 18, wherein applyingthe fifth sensor and applying the sixth sensor includes adjusting therespective tabs so that a distal region of the tabs sits directly abovethe eyebrows without touching the eyebrows.
 20. The method of claim 9,wherein at least one sensor is removable.
 21. The method of claim 9,wherein applying the third sensor includes placing the third sensorbelow a hairline of the subject.
 22. The method of claim 9, wherein theanatomical region of the subject is a nasion of the subject.
 23. Themethod of claim 22, wherein the distance gauge includes an elongatedsection extending from the fourth sensor and applying the fourth sensorincludes positioning the distance gauge so that a distal portion of thedistance gauge is directly above the nasion of the subject.
 24. Aheadset for detecting brain electrical activity comprising: a flexiblesubstrate dimensioned to fit a forehead of a human subject having afirst end and a second end, wherein the first end and the second endeach includes a securing device configured to engage an ear of thesubject to position the flexible substrate across the forehead; a firstsensor disposed on the flexible substrate and configured to contact anupper center region of the forehead when the headset is positioned onthe subject; a second sensor disposed on the flexible substrate andconfigured to contact a lower center region of the forehead when theheadset is positioned on the subject; a third sensor disposed on theflexible substrate and configured to contact a left frontal region ofthe forehead when the headset is positioned on the subject, wherein theheadset is adjustable such that the position of the third sensor ismovable relative to the position of the first sensor; a fourth sensordisposed on the flexible substrate and configured to contact a rightfrontal region of the forehead when the headset is positioned on thesubject, wherein the headset is adjustable such that the position of thefourth sensor is movable relative to the position of the first sensor; afifth sensor disposed on the flexible substrate and configured tocontact a left side region of the forehead when the headset ispositioned on the subject; a sixth sensor disposed on the flexiblesubstrate and configured to contact a right side region of the foreheadwhen the headset is positioned on the subject; a seventh sensor disposedon the first end of the flexible substrate and configured to contact aleft ear region of the subject when the headset is positioned on thesubject; and an eighth sensor disposed on the second end of the flexiblesubstrate and configured to contact a right ear region of the subjectwhen the headset is positioned on the subject, wherein the secondsensor, the third sensor, and the fourth sensor each includes anelongated portion having a first end connected to the sensor and a freeend extending from the sensor.
 25. A method of applying the headset ofclaim 24, the method comprising: positioning the free end of theelongated portion of the second sensor at a nasion region of the subjectto align the second sensor and the first sensor on the forehead;adjusting the location of the first sensor so that the first sensor islocated on the forehead below a hairline of the subject; attaching thefirst sensor and the second sensor to the forehead of the subject;engaging the first end with a first ear region of the subject; engagingthe second end with a second ear region of the subject; attaching theseventh sensor to the first ear region and attaching the eighth sensorto the second ear region; positioning the free end of the elongatedportion of the third sensor directly above a first eyebrow of thesubject so that the free end does not touch the first eyebrow andattaching the third sensor to the forehead of the subject; positioningthe free end of the elongated portion of the fourth sensor directlyabove a second eyebrow of the subject so that the free end does nottouch the second eyebrow and attaching the fourth sensor to the foreheadof the subject; attaching the fifth sensor to the forehead of thesubject; and attaching the sixth sensor to the forehead of the subject.